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UCC27531: UCC27531 Failed with OUTH floating.

Arron Lee
Prodigy 20 points
Part Number: UCC27531

Hello,


We have a circuit in which we utilize only the OUTL of a UCC27531, the OUTH was left floating. We had the UCC27531 fail, it was pulling VDD low, OUTL short to GND and OUTH short to VDD.

Is there a requirement to not float OUTH?

OUTL was only sinking 24mA or blocking 24V max. Vdd was 24V. No evidence of VDD exceeding 24V.

Thank You

Arron

  • 0
    TI__Intellectual 2910 points
    Hi Arron,

    Thank you for choosing UCC27531 for your application. I regret learning that you are experiencing issues. My first reaction is that there should not be a failure introduced based on my understanding of how you are using the device. In order to help diagnose what you are seeding, please:

    1. Confirm how the device terminals are connected. My understanding is that the UCC27531 OUTL is being used as a pull-down only. If available, please share the schematic of this area of your board for betters understanding on my end.
    2. What i s the load connected to OUTL?
    2. Describe when the failure occur -- does the circuit operate at all, or fail immediately when powered? Or does it run for a while (how long) before failure? If possible, please provide oscilloscope capture of the time when the device fails.

    Regards,

    - Daniel
  • 0 in reply to Daniel Ruiz
    Prodigy 20 points
    Hello Daniel,

    I am assisting a colleague with this matter, i have been shown the schematic but do not have a copy.

    It ran for some time without problem. Its logic is driven through an isolator. Its load consisted of a 24V pull up through a 1k Ohm resistor feeding a 22V zener diode on the OUTL pin. The failure occurred after the micro-controller was reprogrammed in circuit, however the board has isolated logic and power. OUTH was floating, pin not routed. All other pins connected as per the recommendations in data sheet.

    It is possible that the logic line had a high frequency signal appear during the programing event, however this should have been buffered by the isolator. All voltages would have been within limits. Is it possible the high frequency (100MHz) switching of the 24mA caused failure?

    Thank You
    Arron